1. Technical Field
The present invention relates to a projection optical system and a projector including the same capable of switching the aspect ratio of a projected image, and in particular, to a projection optical system and a projector in which an optical unit for aspect ratio conversion is detachably mounted.
2. Related Art
As a converter for aspect ratio conversion which is used in a projection optical system of a projector, there is a front-disposed converter which is retreatably disposed at a front position of an existing projection optical system, that is, in front of the image side.
This kind of converter is provided as an external optical unit which is independent of a projector body, causing an increase in size of the projector, complicating adjustment of the entire projection optical system including the converter, or significantly deteriorating an image.
As a converter for aspect ratio conversion which is used in an image-taking optical system, such as a camera, instead of a projection optical system of a projector, there is a rear-disposed anamorphic converter or anamorphic image-taking system which is disposed on the image side of an image-formation optical system (see JP-A-2005-300928 and JP-T-2008-511018). The anamorphic converter described in JP-A-2005-300928 has a first lens unit, a second lens unit which includes an anamorphic lens, and a third lens unit which has positive optical power. The second lens unit is movable between a first state where the second lens unit is disposed at an operation position between the first lens unit and the third lens unit, and a second state where the second lens unit is retreated from the operation position. The anamorphic image-taking system described in JP-T-2008-511018 has a plurality of lens components which have power in different directions.
The anamorphic converter described in JP-A-2005-300928, or the like is used in an image-taking optical system, and if this is used directly in a projection optical system, various restrictions occur. For example, in the image-taking optical system described in JP-A-2005-300928, it is basically assumed that lenses are replaceable, and when no anamorphic converter is used, the image-formation optical system is fixed directly to an image-taking unit and used alone. For this reason, in order to maintain the performance of the image-formation optical system, the anamorphic converter should be extended. Meanwhile, in a projection optical system of a projector, since lens replacement is not generally carried out, a function as a general-purpose converter in which various replacement lenses are mountable is not required.
While it is common knowledge that tilting is generally used (a display panel is offset or shifted in a direction perpendicular to a lens optical axis) in a projection optical system, in an image-taking optical system, since this function is not required, countermeasures or the like against the problem of tilting, for example, positional deviation of an image on the screen when the anamorphic converter is inserted in a tilt state have not been considered at all.